The Chainsong 2006 is encoded with HDCD compatible peak extensions. My own development allows to use them while being able to stay to up-to-date noise shaping technics, which original HDCD hardware didn't have at all.
This is still in a beta stage, so if you have HDCD capable DAC's, any feedback how well it works, or if it doesn't work at all, is highly appreciated.
The other mastered chainsongs are a bit older, thus they don't have this feature.